The present invention relates in general to controlling a variable speed pump for a coolant system of an internal combustion engine, and, more specifically, to minimizing energy consumption for operating the pump while maintaining a minimum required flow for each component connected in the coolant loop.
Because of their high operating temperatures, internal combustion engines require the use of a cooling system to dissipate heat through a radiator. Requirements for the coolant system include rapid warming of a cold engine, removing excess heat from the engine, and supplying heat to components that use the heat such as a heater core for cabin warming, or a heat recovery device of a type that may generate electricity (e.g., exhaust based or manifold based) or that cools exhaust gases for an exhaust gas return (EGR) valve.
A coolant pump (often called the water pump) is typically mechanically driven from the output of the internal combustion engine. A pump has been conventionally sized to give a pumping capacity (i.e., flow rate) sufficient to meet maximum requirements.
Electric pumps have been considered in order to lower the load on the engine at times when no flow or low flow is needed in the coolant loop. Electric pumps are also used on hybrid gas-electric vehicles for the additional reason that a coolant flow may be needed during times that the vehicle is operating off of the battery and the internal combustion engine is off (e.g., to provide cabin heating from an electric heater or to cool a battery or fuel cell).
An electric pump can be operated at variable speeds in order to lower its energy consumption during times that the need for coolant flow is lower. However, prior coolant systems for modulating flow have been complex and expensive (e.g., by requiring additional flow control valves, sensors, and complex control strategies). Copending U.S. patent application Ser. No. 13/534,401, filed Jun. 27, 2012, discloses an invention for reducing power consumption of an electric water heater while maintaining adequate flow for all components in a simple and efficient manner.
The needs of each particular heat-transfer node are determined according to various factors including the amount of heat needing to be lost or gained and the temperature of the coolant. The resulting requests for each node are given in terms of the flow rate of coolant that satisfies the particular needs. However, it is complex and expensive to directly measure the flow rate being delivered by the electric pump. Instead, the typical electric water pump has been controlled based on pump speeds that are usually higher than what is needed but are guaranteed to always meet the minimum requirements. It would be desirable to obtain accurate control of the flow rate delivered by the coolant pump even in the presence of changing flow conditions within the cooling system so that greater energy savings can be realized.